Using QML Modules with Plugins

QML modules may use plugins to expose components defined in C++ to QML applications. Qt Design Studio cannot load the plugins to determine the details of the contained components, and therefore, the modules must provide extra type information for code completion and the semantic checks to work correctly.

To create a QML module and make it appear in the Library view in the Design mode:

  1. Create custom QML controls and place all the .qml files in a directory dedicated to your module. For example: imports\asset_imports.
  2. For Qt Quick UI projects (.qmlproject), specify the path to the directory that contains the module in the .qmlproject file of the application where you want to use the module as a value of the importPaths variable. For example importPaths: [ "imports", "asset_imports" ].
  3. Create a qmldir file for your module and place it in the module directory. For more information, see Module Definition qmldir Files.
  4. Create a qmltypes file, preferably using qmlplugindump. For more information see, Generating qmltypes Files.
  5. Create a directory named designer in your module directory.
  6. Create a .metainfo file for your module and place it in the designer directory. Meta information is needed to display the components in the QML Types tab in Library. Use a metainfo file delivered with Qt, such as qtquickcontrols2.metainfo, as an example.
  7. Build your module using the same Qt version and compiler as Qt Design Studio. For more information, see Running QML Modules in Design Mode.

Your module should now appear in the QML Imports tab in Library in the Design mode. Your components should appear in the QML Types tab if a valid .metainfo file is in place.

Generating qmltypes Files

Ideally, QML modules have a plugins.qmltypes file in the same directory as the qmldir file. The qmltypes file contains a description of the types exported by the module's plugins and is loaded by Qt Design Studio when the module is imported.

For Qt 4.8 and later, one or more qmltypes files can be listed in the qmldir file under the typeinfo header. These files will be read in addition to plugins.qmltypes. For more information, see Writing a qmltypes File.

You can create and edit qmltypes files manually, but you are recommended to use the qmlplugindump tool shipped with Qt 4.8 and later to generate them automatically.

Once you have obtained qmlplugindump for the Qt version the QML module's plugins were compiled with, run the following command to load My.Module version 1.0 from /import/path/my/module including all its plugins and output a description of the plugins' types to /import/path/my/module/plugins.qmltypes:

qmlplugindump -nonrelocatable My.Module 1.0 /import/path > /import/path/my/module/plugins.qmltypes

You can safely ignore the debug output.

Dumping Plugins Automatically

If a module with plugins lacks the qmltypes file, Qt Design Studio tries to generate a temporary file itself by running the qmldump program in the background. However, this automatic dumping is a fallback mechanism with many points of failure and you cannot rely upon it.

Running QML Modules in Design Mode

A QML emulation layer (also called QML Puppet) is used in the Design mode to render and preview images and to collect data. To be able to render custom types correctly from QML modules, the emulation layer must be built with the same Qt version and compiler as the QML modules.

On Windows, select Help > About Qt Design Studio to check the Qt version and compiler that you need to use to build your plugin. For example: Based on Qt 5.15.2 (MSVC 2019, 64 bit).

On macOS, select Qt Design Studio > About Qt Design Studio to see something like: Based on Qt 5.15.2 (Clang 10.0 (Apple), 64 bit).

A plugin should behave differently depending on whether it is run by the emulation layer or an application. For example, animations should not be run in the Design mode. You can use the value of the QML_PUPPET_MODE environment variable to check whether the plugin is currently being run by an application or edited in the Design mode.

If you want to use a different module in the Design mode than in your actual application for example to mockup C++ items, then you can use QML_DESIGNER_IMPORT_PATH in the .pro file (for qmake projects), or declare and set the property qmlDesignerImportPaths in your product (for Qbs projects). Modules in the import paths defined in QML_DESIGNER_IMPORT_PATH will be used only in the Design mode. For an example, see Qt Quick Controls - Contact List.

Available under certain Qt licenses.
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